java计算两个string类型日期的天数差

可以使用Java中的日期时间类`LocalDate`来计算两个字符串类型日期的天数差。

示例代码如下：

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;

public class DateUtils {
    public static long daysBetween(String start, String end) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDate startDate = LocalDate.parse(start, formatter);
        LocalDate endDate = LocalDate.parse(end, formatter);
        return ChronoUnit.DAYS.between(startDate, endDate);
    }
}

使用示例：

public class Main {
    public static void main(String[] args) {
        String start = "2021-01-01";
        String end = "2021-02-01";
        long days = DateUtils.daysBetween(start, end);
        System.out.println("Days between " + start + " and " + end + ": " + days);
    }
}

输出结果为：

Days between 2021-01-01 and 2021-02-01: 31